Download Capturing Greenhouse Gases

SLEIPNER
NATURAL
GAS RIG
NORTH SEA
Capturing
Greenhouse Gases
by Howard Herzog, Baldur Eliasson and Olav Kaarstad
UTSIRA FORMATION
Sequestering carbon dioxide underground
or in the deep ocean could help alleviate
concerns about climate change
T
he debate over climate change has shifted. Until very recently, scientists still deliberated
whether human activity was altering the global
climate. Specifically, was the release of greenhouse gases,
which trap heat radiating from the earth’s surface, to
blame? With scientific evidence mounting in favor of the
affirmative, the discussion is now turning to what steps
society can take to protect our climate.
One solution almost certainly will not succeed: running out of fossil fuels—namely, coal, oil and natural gas.
Morris Adelman, professor emeritus at the Massachusetts Institute of Technology and expert on the economics of oil and gas, has consistently made this point for 30
years. In the past century and a half, since the beginning
of the industrial age, the concentration of carbon dioxide
in the atmosphere has risen by almost one third, from
280 to 370 parts per million (ppm) — primarily as a result
of burning fossil fuels. In the 1990s, on average, humans
NATURAL GAS
PIPELINES
NATURAL GAS
Copyright 2000 Scientific American, Inc.
DEEP UNDERGROUND, some 1,000 meters below the
bottom of the North Sea, carbon dioxide is pumped into
the sandstone reservoir known as the Utsira Formation,
where it can be stored for thousands of years. To avoid
Norway’s carbon dioxide tax, the owners of the Sleipner
natural gas rig, located some 240 kilometers from the Norwegian coast, now bury the greenhouse gas that would
otherwise be released from the rig into the atmosphere.
discharged 1.5 ppm of carbon dioxide annually; with
each passing year, the rate increased. Even though humans release other greenhouse gases, such as methane
and nitrous oxide, experts project that carbon dioxide
emissions will account for about two thirds of potential
global warming. As apprehension has grown regarding the
possible hazards of a changing global climate, environmental groups, governments and certain industries have
been trying to reduce the level of greenhouse gases in the atmosphere, often by promoting energy efficiency and alternative energy sources— for instance, wind or solar power.
Realistically, however, fossil fuels are cheap and plentiful and will be powering our cars, homes and factories
well into the 21st century and possibly beyond. Worries
about diminishing fuel supplies have surfaced periodically
over the past 100 years, but continuing improvements in
both oil exploration and production technology should
keep the fuel flowing for decades to come. Furthermore,
since the adoption of the first international treaty de-
Copyright 2000 Scientific American, Inc.
signed to stabilize greenhouse gas emissions, signed at
the 1992 Earth Summit in Rio de Janeiro, the global demand for fossil fuels has actually increased. Today more than 85 percent of the
world’s commercial energy needs are supplied by fossil fuels. Although policies that promote energy efficiency and alternative energy sources are crucial to mitigating climate
change, they are only one part of the solution.
Indeed, even if society were to cut back the use of fossil
fuels today, the planet would still most likely experience
significant repercussions as a result of past emissions. The
climate’s response time is slow, and carbon dioxide remains in the atmosphere for a century or more if left to
nature’s devices. Therefore, we must have a portfolio of
technology options to adequately reduce the accelerating
buildup of greenhouse gases. Significant research and development efforts are already exploring ways to improve
energy efficiency and increase the use of fuels with no car-
Scientific American February 2000
73
DAVID FIERSTEIN
CARBON DIOXIDE
INJECTION WELL
STORING CARBON DIOXIDE
UNDERGROUND AND IN THE OCEAN
CARBON DIOXIDE
PUMPING STATION
CARBON DIOXIDE
PUMPING STATION
TOWED PIPE
PIPELINE
DRY ICE
PIPELINES
UNMINABLE
COAL BEDS
1,000 m
DEPLETED OIL OR
GAS RESERVOIRS
DROPLET PLUME
2,000 m
MINED SALT DOME
3,000 m
DEEP AQUIFER
CARBON DIOXIDE
LAKE
STORAGE UNDERGROUND ADVANTAGES
DISADVANTAGES
STORAGE IN OCEAN ADVANTAGES
DISADVANTAGES
Coal Beds
Mined Salt Domes
Deep Saline Aquifers
Depleted Oil or Gas
Reservoirs
Immature technology
High costs
Unknown storage integrity
Limited capacity
Droplet Plume
Towed Pipe
Dry Ice
Carbon Dioxide Lake
Some leakage
Some leakage
High costs
Immature technology
STORAGE SITES for carbon dioxide in the ground and deep sea
should help keep the greenhouse gas out of the atmosphere where it
bon content (renewable energy sources
or nuclear power). But a third approach
is attracting notice as people recognize
that the first two options will simply not
be sufficient: carbon sequestration, the
idea of finding reservoirs where carbon
dioxide can be stored rather than allowing it to build up in the atmosphere.
Our strategy may surprise some readers. Sequestering carbon is often connected to planting trees: trees (and vegetation in general) absorb carbon dioxide
from the air as they grow and hold on to
that carbon for their lifetime [see box on
page 77]. Scientists estimate that, all together, plants currently retain about 600
gigatons of carbon, with another 1,600
gigatons in the soil.
Plants and soils could perhaps sequester another 100 gigatons or more of
carbon, but additional sinks will be
needed to meet the challenge of escalating greenhouse gas emissions. So during
74
Minimal environmental effects
Minimal environmental effects
Simple technology
Carbon will remain in ocean
for thousands of years
now contributes to climate change. The various options must be
scrutinized for cost, safety and potential environmental effects.
the past 10 years, the three of us have
explored another possibility: capturing
carbon dioxide from stationary sources—
for example, a chemical factory or an
electric power plant— and injecting it
into the ocean or underground. We are
not alone in our efforts but are part of a
worldwide research community that includes the International Energy Agency
(IEA) Greenhouse Gas Research and Development Program, as well as government and industry programs.
A New Approach in Norway
S
leipner offshore oil and natural gas
field is in the middle of the North
Sea, some 240 kilometers off the coast
of Norway. Workers on one of the natural gas rigs there inject 20,000 tons of
carbon dioxide each week into the pores
of a sandstone layer 1,000 meters below
the seabed. When the injection at Sleip-
ner began in October 1996, it marked
the first instance of carbon dioxide being stored in a geologic formation because of climate considerations.
How did this venture come about?
One reservoir at Sleipner contains natural gas diluted with 9 percent carbon
dioxide— too much for it to be attractive
to customers, who generally accept no
more than 2.5 percent. So, as is common practice at other natural gas fields
around the world, an on-site chemical
plant extracted the excess carbon dioxide. At any other installation, this carbon
dioxide would simply be released to the
atmosphere. But the owners of the Sleipner field—Statoil (where one of us, Kaarstad, works as a researcher), Exxon,
Norsk Hydro and Elf— decided to sequester the greenhouse gas by first compressing it and then pumping it down a
well into a 200-meter-thick sandstone
layer, known as the Utsira Formation,
Capturing Greenhouse Gases
Scientific American February 2000
Copyright 2000 Scientific American, Inc.
DAVID FIERSTEIN
Potentially low costs
Custom designs
Large capacity
Proven storage integrity
which was originally filled with saltwater. The nearly one million tons of carbon dioxide sequestered at Sleipner last
year may not seem large, but in the small
country of Norway, it amounts to about
3 percent of total emissions to the atmosphere of this greenhouse gas.
The principal motivation for returning
carbon to the ground at Sleipner was the
Norwegian offshore carbon dioxide tax,
which in 1996 amounted to $50 for
every ton of the gas emitted (as of January 1, 2000, the tax was lowered to $38
per ton). The investment in the compression equipment and carbon dioxide
well totaled around $80 million. In
comparison, if the carbon dioxide had
been emitted to the atmosphere, the
companies would have owed about $50
million each year between 1996 and
1999. Thus, the savings paid off the investment in only a year and a half.
In other parts of the world, companies
are planning similar projects. In the
South China Sea, the Natuna field contains natural gas with nearly 71 percent
carbon dioxide. Once this field has been
developed commercially, the excess carbon dioxide will be sequestered. Other
studies are investigating the possibility of
storing captured carbon dioxide underground, including within liquefied natural gas installations at the Gorgon field
on Australia’s Northwest Shelf and the
Snøhvit (“Snow White”) gas field in the
Barents Sea off northern Norway, as well
as the oil fields of Alaska’s North Slope.
In all the projects now under way or
in development, carbon dioxide must be
captured for commercial reasons— for
instance, to purify natural gas before it
can be sold. The choice facing the companies involved is therefore between releasing the greenhouse gas to the atmosphere or storing it. They are not deciding whether to collect the carbon dioxide
in the first place. We expect that more
such companies needing to reduce carbon dioxide emissions will opt for sequestration in the future, but convincing
other businesses to capture carbon dioxide emissions from large point sources
such as electric power plants is more
difficult because of the costs associated
with carbon dioxide collection.
Underground or Underwater
T
he technology for pumping carbon
dioxide into the ground is actually
well established— it is essentially the reverse of pumping oil and natural gas
out of the ground. In fact, the practice
is common at many oil fields today. Injecting carbon dioxide into an existing
oil reservoir increases the mobility of
the oil inside and thereby enhances the
well’s productivity. During 1998, U.S.
oil field workers pumped a total of
about 43 million tons of carbon dioxide
into the ground at more than 65 enhanced oil recovery (EOR) projects. Yet
this quantity adds up to comparatively
little carbon sequestration. In contrast,
geologic formations, including saline
aquifer formations (such as that at Sleipner), unminable coal beds, depleted oil
or gas reservoirs, rock caverns and
mined salt domes all around the world,
can collectively hold hundreds if not
thousands of gigatons of carbon.
Although geologic formations show
great promise as storage sites, the largest
potential reservoir for anthropogenic car-
bon dioxide is the deep ocean. Dissolved
in its waters, the ocean holds an estimated 40,000 gigatons of carbon (compared
with 750 gigatons in the atmosphere),
but its capacity is much larger. Even if
humans were to add to the ocean an
amount of carbon dioxide equivalent to
doubling the preindustrial atmospheric
concentration of the gas, it would change
the carbon content of the deep ocean by
less than 2 percent. Indeed, slow-acting,
natural processes will direct about 85
percent of present-day emissions into
the oceans over hundreds of years. Our
idea is to accelerate these events.
For ocean sequestration to be effective, the carbon dioxide must be injected
into the sea below the thermocline— the
layer of ocean between approximately
100 and 1,000 meters, in which water
temperatures decrease dramatically with
THE BASICS
BURYING CARBON DIOXIDE
THE AUTHORS REVIEW CARBON SEQUESTRATION TECHNOLOGY
What is carbon sequestration? The idea is to store the greenhouse gas carbon
dioxide in natural reservoirs rather than allowing it to build up in the atmosphere.
Although sequestering carbon is often connected to planting trees, we are investigating the possibility of capturing carbon dioxide from stationary sources— an
electric power plant,for example— and injecting it into the ocean or underground.
Where exactly will the carbon dioxide be stored? It can be pumped into underground geologic formations,such as unminable coal beds,depleted oil or gas wells,
or saline aquifers,in a process that is essentially the reverse of pumping oil up from
below the earth’s surface.Engineers are also looking into the possibility of bubbling
carbon dioxide directly into the ocean at concentrations that will not affect the surrounding ecosystem and at depths that will ensure it remains in the ocean.
How will scientists make certain it is stored safely? Making sure carbon dioxide
will be stored in a safe and environmentally sound manner is one of our primary
goals. Memories of the 1986 Lake Nyos tragedy in Cameroon (in which a huge
bubble of carbon dioxide erupted from the lake, suffocating some 1,700 people),
raise the issue of safety,particularly for underwater storage.Yet the situation in the
lake was entirely different than the scenario we envision for carbon sequestration
in the ocean.A small lake simply cannot hold a large amount of carbon dioxide, so
the Nyos eruption was inevitable. There are no such limitations in the oceans. In
the case of underground storage, nature has demonstrated a safe track record:
reservoirs such as the McElmo Dome in southwestern Colorado have held large
quantities of carbon dioxide for centuries.
Are there any active carbon sequestration projects today? The Sleipner natural
gas rig off the coast of Norway currently pumps carbon dioxide into a saline
aquifer 1,000 meters below the seafloor. Although Sleipner is the only sequestration project driven solely by climatic change considerations, other commercial
projects demonstrate the technology. More than a dozen power plants capture
carbon dioxide from their flue gas, including the Shady Point, Okla., plant built by
the international engineering company ABB. And at over 65 oil wells in the U.S.,
companies inject the gas underground to enhance the efficiency of oil drilling.
Capturing Greenhouse Gases
Scientific American February 2000
Copyright 2000 Scientific American, Inc.
75
Dissolving in water
Growth
Deforestation
Burning of fossil fuels
NATURAL STORES OF CARBON exist in the atmosphere,
oceans, sediments and biosphere; exchange between these reservoirs occurs in a variety of ways. When humans burn fossil fuels,
depth. The cooler, denser water below
travels extremely slowly up through the
thermocline. Therefore, the water beneath the thermocline may take centuries to mix with the surface waters,
and any carbon dioxide below this
boundary will be effectively trapped. In
general, the deeper we inject the carbon
dioxide, the longer it will take to reach
the atmosphere.
Carbon dioxide can be introduced
into seawater in two ways: dissolving it
at moderate depths (from 1,000 to
2,000 meters) to form a dilute solution
or injecting it below 3,000 meters to create what we call a carbon dioxide lake.
The first strategy seeks to minimize local
environmental effects by diluting the carbon dioxide, whereas the lake approach
tries to maximize the length of time the
carbon dioxide will reside in the ocean.
The concept of storing carbon dioxide
in the ocean can be traced to a 1977 paper by Cesare Marchetti of the International Institute for Applied Systems
Analysis in Laxenburg, Austria, who
suggested that carbon dioxide could be
piped into the waters of the Mediterranean Sea at Gibraltar, where it would
naturally flow out into the Atlantic and
be carried to the deep ocean. Even today
building a pipe along the ocean floor to
76
DAVID FIERSTEIN
Weathering
we transfer carbon originally stored in the deep sediments into the
atmosphere. The goal of carbon sequestration is to redirect carbon from the atmosphere into one of the other three reservoirs.
transport carbon dioxide to an appropriate depth remains one of the more realistic options for carbon sequestration.
Other injection scenarios that have been
suggested include dropping dry ice into
the ocean from ships, introducing carbon dioxide at 1,000 meters through a
pipe towed by a moving ship, and running a pipe down 3,000 meters or more
to depressions in the seafloor.
Safe and Sound?
D
espite the availability of the technology necessary to proceed with
carbon storage in both terrestrial and
oceanic reservoirs, we need to understand better what the consequences for
the environment will be. Obviously, the
process of storing carbon dioxide needs
to be less damaging to the environment
than the continued release of the greenhouse gas. In the case of underground
storage, we must be sure to assess the
long-term stability of any formation under consideration as a reservoir. The
structural integrity of a site is important
not only to ensure that the gas does not
return to the atmosphere gradually but
also because a sudden release of the carbon dioxide in a populated area could be
catastrophic. Carbon dioxide is heavier
than air, and a rapid, massive discharge
of the gas would displace oxygen at the
surface, suffocating people and wildlife.
Fortunately, though, nature has stored
carbon dioxide underground for millions of years in reservoirs such as McElmo Dome in southwestern Colorado, so
we know there are ways to do it safely.
Ocean sequestration presents a different set of challenges. The leading concern is the repercussion it will have on
the acidity of the ocean. Depending on
the method of carbon dioxide release,
the pH of seawater in the vicinity of an
injection site could be between 5 and 7.
(A pH of 7 is considered neutral; the pH
of seawater is normally around 8.)
A large change in acidity could be
harmful to organisms such as zooplankton, bacteria and bottom-dwelling creatures that cannot swim to less acidic waters. Research by one of us (Herzog) and
M.I.T. colleague E. Eric Adams, however,
suggests that keeping the concentration
of carbon dioxide dilute could minimize
or even eliminate problems with acidity.
For example, a dilution factor of one part
per million yields a change in pH of less
than 0.1. This reduced concentration
could easily be achieved by releasing the
carbon dioxide as small droplets from a
pipe on the seafloor or on a moving ship.
Capturing Greenhouse Gases
Scientific American February 2000
Copyright 2000 Scientific American, Inc.
Money Matters
A
long with questions of environmental safety and practicality, we must
look at how much carbon sequestration
will cost. Because electricity-generating
power plants account for about one third
of all carbon dioxide released to the atmosphere worldwide and because such
plants are large, concentrated sources of
emissions, they provide a logical target
for implementing carbon sequestration.
Furthermore, such plants have had experience reducing pollutants in the past.
(Notably, though, attention has primarily
focused on controlling such contaminants as particulate matter, sulfur oxides,
nitrogen oxides or even carbon monoxide— but not on carbon dioxide itself.)
Devices known as electrostatic precipitators, first introduced in the 1910s,
helped to clean up the particles emitted
from burning fossil fuels while raising
the price of electricity only modestly. Today a modern power plant that includes
state-of-the-art environmental cleanup
equipment for particulates, sulfur oxides and nitrogen oxides costs up to 30
percent more to install than a plant
without such equipment. This environmental equipment adds only between
0.1 and 0.5 of a cent per kilowatt-hour
to the price of the electricity generated.
Because the exhaust gases of fossilfueled power plants contain low concentrations of carbon dioxide (typically
ranging from 3 to 15 percent), it would
not be economical to funnel the entire exhaust stream into storage sites. The first
step, therefore, should be to concentrate
the carbon dioxide found in emissions.
Unfortunately, with existing equipment
this step turns out to be the most expensive. Thus, developing technology
that lowers these costs is a major goal.
The most common method for separating carbon dioxide involves mixing a
solution of dilute monoethanolamine
(MEA) with the flue gases inside the absorption tower of a plant designed to
capture the greenhouse gas. The carbon
dioxide in the exhaust reacts with the
MEA solution at room temperature to
form a new, loosely bound compound.
This compound is then heated in a second column, the stripping tower, to approximately 120 degrees C to release
the carbon dioxide. The gaseous carbon
dioxide product is then compressed,
dried, chilled, liquefied and purified (if
necessary); the liquid MEA solution is
recycled. Currently this technology works
well, but it must become more energyefficient if it is to be applied to large-scale
carbon sequestration. Today only a
handful of power plants, including one
built in Shady Point, Okla., by ABB
(where Eliasson serves as head of global
change research), capture carbon dioxide
from their flue gases. The carbon dioxide
PLANT A TREE
ANOTHER OPTION FOR STORING CARBON NEEDS ONLY SUN AND WATER
F
or over a decade, an organized carbon sequestration project has been under
way in the deforested regions and farmlands of Guatemala. No underground
pipes or pumping stations are required— just trees.As the plants grow,they absorb
carbon dioxide from the atmosphere, which they store as carbon in the form of
wood.Hoping to capitalize on this natural vehicle for sequestering carbon,companies and governments have initiated reforestation,afforestation (planting trees on
land not previously forested) and agroforestry (integrating trees with agricultural
crops) efforts as a way to meet obligations set forth in the Kyoto Protocol,the international environmental treaty on lowering greenhouse gas emissions.
In 1988 AES, a U.S.-based electrical company, pioneered the first forestry project
designed to offset carbon dioxide emissions. At the time, AES was about to build a
new coal-fired power plant in Connecticut,which was expected to release 52 million
tons of carbon dioxide during its 40-year life span.Working in Guatemala with the
World Resources Institute (WRI) and the relief organization CARE,AES created community woodlots,introduced agroforestry practices and trained forest-fire brigades.
According to WRI calculations, up to 58 million tons of carbon dioxide will be absorbed over the lifetime of the project.Currently more than a dozen such programs
are under way on some four million hectares of
forest land, including areas in the U.S., Norway,
Brazil,Malaysia,Russia and Australia.
According to recent estimates, forests around
the globe today store nearly one trillion tons of
carbon.Scientists calculate that to balance current
carbon dioxide emissions, people would have to
plant new forests every year covering an area of
land equivalent to the whole of India. Forestry
projects are not a quick-fix solution, but they do
offer many benefits, ranging from better habitats
for wildlife to increased employment. Nevertheless, the potential for trees to serve as a reservoir
for carbon is limited, and the approach has its
drawbacks.Tree plantations drain native plant biodiversity and can disturb local communities, forcing them to relocate.As with many proposed soluSEEDLINGS are planted by tions to climate change,trees will be effective only
workers in Fiji as part of a as one part of a global commitment to reduce
reforestation effort.
greenhouse gas emissions. —Diane Martindale
Capturing Greenhouse Gases
Scientific American February 2000
Copyright 2000 Scientific American, Inc.
PETER ARNOLD, INC.
Over the next several years, the scientific community will be conducting a
number of experiments to assess how
large amounts of carbon dioxide can be
stored in a safe and environmentally
sound manner. In the summer of 2001,
for instance, a team of researchers from
the U.S., Japan, Switzerland, Norway,
Canada and Australia will begin a study
off the Kona Coast of Hawaii to examine the technical feasibility and environmental effects of carbon storage in the
ocean. (Two of us are participating in
this project, Herzog as a member of the
technical committee and Eliasson as a
member of the steering committee.)
Our plan is to run a series of about 10
tests over a period of two weeks, involving the release of carbon dioxide at a
depth of 800 meters. We will be monitoring the resulting plume and taking
measurements, including the pH of the
water and the amount of dissolved inorganic carbon. These data will allow us
to refine computer models and thereby
generalize the results of this experiment
to predict environmental responses more
accurately. We are also interested in what
technical design works best to rapidly dilute the small droplets of carbon dioxide.
77
A BREAKTHROUGH IN CLIMATE CHANGE POLICY?
BY DAVID W. KEITH AND EDWARD A. PARSON
tabilizing the carbon dioxide concentration at 550 parts per million (ppm) —
double the preindustrial level— is widely
considered an ambitious target for emissions control.Yet this concentration will still
cause substantial climate change.The resulting environmental problems, however, will
most likely have only a small effect on the
world’s overall economic output; rich countries in particular should emerge relatively
unscathed. But the results for specific regions will be more pronounced, with some
places benefiting and others suffering. For
instance,although parts of the northern U.S.
may enjoy warmer winters, entire ecosys-
S
78
tems, such as the southwestern mountain technologies are already available and apforests, alpine meadows and certain coastal pear to be significantly cheaper than reforests, may disappear from the continental newables for generating electricity. To
U.S. These likely consequences— and more achieve deep reductions in greenhouse
important, the possibility of unanticipated gas emissions, however, society must also
changes— are compelling reasons to try to start using carbon-free fuels, such as hydrostabilize concentrations below 550 ppm,if it gen,for transportation.Here the relative adcan be done at an acceptable cost.
vantage of carbon management over reAt present,the cost of holding concentra- newables is even greater than in producing
tions to even 550 ppm through convention- electricity.Furthermore, these technologies
al means appears high, both in dollars and offer one significant advantage over alterin other environmental problems. All non- native energy sources: because they are
fossil-fuel energy sources available today more compatible with the existing energy
are expensive,and renewable
sources have low power denCosts of Reducing Carbon
sities: they produce relatively
$75
little power for the amount of
Current solar power
land required.Large-scale use
of renewable energy could
EFFICIENCY
IMPROVEMENTS
thereby harm our most precious environmental resource:
$50
land. Although technological
advances should reduce the
cost of renewables, little can
be done to improve their
Current wind power
power densities,which are in$25
trinsic to the sources.
Coal
So must we conclude that
reducing carbon emissions
CARBON
MANAGEMENT Natural gas
without causing other unacceptable environmental im0
0
25
50
75
pacts will deliver a massive
Carbon
Dioxide
Emissions
economic blow? Not neces(kilogram of carbon per gigajoule of energy)
sarily. The crux of the cost
problem is predicting how
REDUCING CARBON DIOXIDE EMISSIONS by
fast money-saving technical
switching from coal to natural gas can save money. The
advances might develop in
authors argue that further reductions will be cheaper to
response to a carbon tax or
make by carbon management (green) than by solar power or by extreme efficiency improvements (blue). Alsome other form of regulathough wind power is relatively cheap, the land area retion.Notably,most economic
quired may preclude its widespread use.
models used today to assess
the cost of reducing emissions assume that innovation proceeds at infrastructure, we expect their costs to fall
its own pace and cannot be accelerated by more quickly than those of renewables.
Carbon management weakens the link
policy. Under this assumption, delaying efforts to cut emissions makes sense because between burning fossil fuels and releasing
it will allow time to develop better technol- greenhouse gases, making the world’s ecoogy that will lower the cost of reductions. nomic dependence on fossil fuels more susUnder the contrary assumption— which we tainable. This gives carbon management a
regard as closer to the truth— innovation re- crucial advantage: by reducing the threat to
sponds strongly to price and policy signals. fossil-fuel industries and fossil-fuel-rich naIn this case, early policy action on climate tions, carbon management may ease curchange is advantageous, because it would rent political deadlocks. Stated bluntly, if sostimulate the innovations that reduce the ciety adopts carbon management widely,
existing fossil-fuel-dependent industries and
cost of making large emission reductions.
Carbon management may be just such nations may continue to operate profitably
an innovation.Certain carbon management both in present energy markets and in new
Capturing Greenhouse Gases
Scientific American February 2000
Copyright 2000 Scientific American, Inc.
DAVID FIERSTEIN
Electricity Cost (dollars per gigajoule)
s a result of human activities, the atmospheric concentration of carbon dioxide has increased by 31 percent over the
past two centuries. According to businessas-usual projections, it will reach twice the
preindustrial level before 2100. Although
there is little doubt that this increase will noticeably transform the climate, substantial
uncertainties remain about the magnitude,
timing and regional patterns of climate
change; even less is known about the ecological,economic and social consequences.
Despite these uncertainties, an international consensus has emerged regarding
the importance of preventing runaway levels of carbon dioxide in the atmosphere.An
effort to stabilize the concentration of carbon dioxide at even double its preindustrial level— generally considered the lowest
plausible target— will require reducing
global carbon dioxide emissions by about
50 percent from projected levels by 2050.
Not surprisingly,such an extreme reduction
will require a fundamental reorganization
of global energy systems.
Most current assessments of greenhouse
gas emissions assume that the reductions
will be achieved through a mix of increasing
energy efficiency and switching to nonfossil-fuel alternative energy sources, such as
solar, wind, biomass or nuclear. In the accompanying article,“Capturing Greenhouse
Gases,”the authors review a radically different approach: burning fossil fuels without
releasing carbon dioxide to the atmosphere
by separating the carbon emissions and
burying them underground or in the deep
ocean. We believe this approach— termed
carbon management— has fundamental
implications for the economics and politics
of climate change.
A
erhaps even more disconcerting for environmentalists, though, is that carbon
management collides with a deeply rooted
belief that continued dependence on fossil
fuels is an intrinsic problem, for which the
only acceptable solution is renewable energy. Carbon management was first proposed
as “geoengineering,” a label it now shares
with proposals to engineer the global climate, for example, by injecting aerosols into
the stratosphere to reflect solar radiation and
cool the earth’s surface.Many environmentalists hold a reasonable distaste for large-scale
technical fixes, arguing that it would be better to use energy sources that do not require
such massive clean-up efforts.
Carbon management is a promising technology, but it remains unproved. And caution is certainly wise: the history of energy
technologies is littered with options once
touted as saviors that now play at most minor roles (for example, nuclear energy). Exploring the potential of either carbon management or renewable energy will require
political and economic action now— that is,
greater support for basic energy research
and carbon taxes or equivalent policy measures that give firms incentives to develop
and commercialize innovations that reduce
emissions at a reasonable cost.It may be that
carbon management will allow the world—
at long last— to make deep cuts in carbon
dioxide emissions at a politically acceptable
cost. Indeed, for the next several decades,
carbon management may be our best shot
at protecting the global climate.
P
DAVID W.KEITH and EDWARD A.PARSON often collaborate on environmental policy research.Keith is an assistant professor in the department of engineering and public policy at
Carnegie Mellon University. Parson is an associate professor at the John F.Kennedy School of
Government at Harvard University.
ABB CORPORATE RESEARCH
markets that develop around carbon management,making them more willing to tolerate policies that pursue substantial reduction
of atmospheric emissions.
Environmentalists, however, are likely to
find carbon management profoundly divisive for several reasons.Carbon sequestration
is only as good as the reservoirs in which the
carbon is stored. The unfortunate history of
toxic and nuclear waste disposal has left
many reasonable people skeptical of expert
claims about the longevity of underground
carbon disposal. As researchers assess the
safety of proposed carbon reservoirs both
underground and in the ocean, they must
address such skepticism evenhandedly.
is then sold for commercial applications, such as freeze-drying chicken or
carbonating beer and soda.
Another application for captured carbon dioxide offers a number of possible
benefits. Methanol can be used as fuel
even now. Generating this cleaner source
of energy from captured carbon dioxide
and hydrogen extracted from carbonfree sources would be more expensive
than producing methanol from natural
gas, as is currently done. But by reusing
carbon dioxide—and by giving it a market value—this procedure ought to reduce overall emissions, provide an incentive to lower the costs of carbon
dioxide–capture technology and help
start a transition to more routine use of
cleaner fuels.
Scientists, policymakers and the public
must deal with the continuing importance of coal, oil and natural gas as a
source of energy, even in a world constrained by concerns about climate
change. The basic technology needed to
use these fuels in a climate-friendly manner does exist. Current equipment for
capturing carbon dioxide from power
plants would raise the cost of generating
electricity by 50 to 100 percent. But because sequestration does not affect the
cost of electricity transmission and distribution (a significant portion of consumers’ electricity bills), delivered prices
will rise less, by about 30 to 50 percent.
Research into better separation technologies should lead to lowered costs.
What needs to happen for carbon sequestration to become common prac-
CAPTURE PLANT located in Shady Point,
Okla., separates carbon dioxide from its
exhaust fumes; the gas is then sold for use
in the food industry.
tice? First, researchers need to verify the
feasibility of the various proposed storage sites, in an open and publicly acceptable process. Second, we need leadership from industry and government to
demonstrate these technologies on a
large enough scale. Finally, we need improved technology to reduce costs associated with carbon dioxide separation
from power plants. The Sleipner project
has shown that carbon sequestration
represents a realistic option to reduce
carbon dioxide emissions when an economic incentive exists. During the past
100 years, our energy supply system has
undergone revolutionary changes— from
a stationary economy based on coal and
steam to a mobile economy based on liquid fuels, gas and electricity. The changes
over the next 100 years promise to be no
SA
less revolutionary.
The Authors
HOWARD HERZOG, BALDUR ELIASSON and OLAV KAARSTAD met in Amsterdam
in March 1992 at the First International Conference on Carbon Dioxide Removal. Herzog,
a principal research engineer at the Massachusetts Institute of Technology Energy Laboratory, is the primary author of a 1997 U.S. Department of Energy White Paper on carbon sequestration. Eliasson, head of ABB’s Energy and Global Change Program, is the Swiss representative to as well as vice chairman of the International Energy Agency’s Greenhouse Gas
Research and Development Program. Kaarstad, principal research adviser in the area of energy and environment at the Norwegian oil and gas company Statoil, is currently involved
in the ongoing carbon dioxide–injection project at the Sleipner field in the North Sea.
Further Information
ABB Group’s Energy and Global Change Web site is at www.abb.com/ (click on “Environment,” then on “Energy and Global Change”).
IEA Greenhouse Gas Research and Development Program Web site is at www.ieagreen.org.uk/
M.I.T. Energy Laboratory Web site is at web.mit.edu/energylab/www
Statoil Web site is at www.statoil.com (for information on the Sleipner area in particular, go
to www.statoil.com/statoilcom/svg00990.nsf/ealias/Sleipner).
U.S. Department of Energy’s Office of Fossil Energy Web site is at www.fe.doe.gov/
coal_power/sequestration/
U.S. Department of Energy’s Office of Science Web site is at www.sc.doe.gov/production/
ober/carbseq.html
Capturing Greenhouse Gases
Scientific American February 2000
Copyright 2000 Scientific American, Inc.
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